The present invention relates to lawn mowers and, in particular, to lawn mowers mounted on castor wheels.
Household lawn mowers comprise a cutting deck upon which is mounted a motor. The motor can be either an electric motor powered by either a mains electricity supply or a battery or an internal combustion engine. The motor rotatingly drives a cutting blade mounted below the cutting deck about a substantially vertical axis, which cuts the grass beneath the deck as it rotates. The cutting deck is commonly mounted on wheels or rollers, having a fixed direction of travel so that the lawn mower moves over the lawn in a forward and reverse direction.
It is desirable to have the height of the cutting blade adjustable in relation to the surface of the lawn which allows the grass to be cut to differing heights. One common way of achieving this is by having the cutting deck of the lawn mower mounted on the wheels or rollers in such a manner that the height of the deck, and hence the height of the cutting blade, is adjustable relative to the wheels.
Such mechanisms include mounting the axles of the wheels or rollers on the ends of levers which are pivotally mounted onto the deck and which are capable of being releasably locked into a plurality of angular positions. The height of the cutting deck in relation to the wheels or rollers is dependent upon the angle of pivot of the levers. Interconnecting bars can be added between the levers to ensure that the height adjustment of interconnected wheels is uniform.
In order to increase the maneuverability of the mower, it is known to mount the cutting deck of a lawn mower on castor wheels which can freely swivel through 360.degree. instead of wheels or rollers which have a predetermined fixed direction of travel. This allows the cutting deck of the mower to travel in any direction, both linearly and rotationally.
It is desirable to mount the cutting deck on the castor wheels in such a manner that the height of the cutting deck in relation to the surface of the lawn is adjustable in a similar fashion to that of mower having the cutting deck mounted on wheels which have a fixed direction of travel. However, the mechanisms which are commonly used to mount standard wheels so that they are adjustable in height cannot be utilized to mount castor wheels in a similar manner. This is due to the requirement of having to maintain the axes of swivel of the castor wheels vertical regardless of the height setting of the castor wheels in relation to the cutting deck.
AU 24874/97 discloses a lawn mower having a cutting deck mounted on castor wheels. The height of the deck is adjustable relative the castor wheels. The height adjustment mechanism comprises two parallel levers which are both pivotally attached to the deck at one end and which are also both pivotally attached to the stem of the castor wheel at the other end. The two levers form a parallelogram with the stem of the castor wheel and the deck such that the stem and thus the axis of swivel of the castor wheel remains vertical regardless of the angular position of the two levers. A rotatable threaded shaft is provided for adjusting and maintaining the angular position of the two levers.
However, the design of the height adjustment mechanism disclosed in AU 24874/97 is complicated and requires a substantial amount of space to provide a sufficiently large region through which the castor wheel can sweep to allow it to travel through its full range of pivot.